1. Field of the Invention
The present invention relates to a traffic shaper for absorbing the cell delay variation in virtual paths (Virtual Path: VP) and virtual channels (Virtual Channel: VC) in an ATM (asynchronous transmission mode) network.
2. Description of the Related Art
Data to be transmitted is devided into a plurality of fixed-length packets, each packet is called xe2x80x9ca cellxe2x80x9d, and those cells are transmitted in the ATM network. On a physical transmission line of the ATM network, virtual paths and virtual channels are defined for each of connections, and cells on virtual channels are multiplexed and transmitted on a virtual path.
As cells are multiplexed asynchronously, when cells pass through a multiplexing apparatus, a switch apparatus and so on, a cell delay variation (hereinafter called CDV) occurs due to the deference of queueing time in buffers in each apparatus. The CDV may cause to generate cells, each having a small cell interval, and as the result, the traffic becomes a burst condition so the coefficient of utilization of the network resources lowers.
For solving the above problem, a traffic shaper is proposed. The traffic shaper is provided for removing the CDV in multiplexed cells on virtual paths or virtual channels and shaping the cell intervals. In this traffic shaper, input cells are once stored in a buffer memory and a timing is adjusted for outputting a cell so as to have the cell interval requirede by a destination apparatus.
However, the traffic shaper dealing with plural virtual paths or virtual channels is further required a function of an output competition control. This is because that there occurs a case that cells of different virtual paths or virtual channels are present at the same output timing. The output competition control of cell is therefore required when cells of plural virtual paths or virtual channels are multiplexed and output to the transmission path. A CDV is still added at the time of the output competition control operation though it is smaller than that before inputting to the traffic shaper.
As conventional control methods of the output competition controls of cell, there are an FIFO (First In, First Out) rule and a round robin method. But, they are not considering the traffic characteristics of the virtual path or virtual channel in their control.
Among the traffic characteristics, the CDV greatly affects the coefficient of utilization of the network resources and the quality of services (hereinafter called QOS) of the virtual path or virtual channel. But in case of the output competition control which does not consider the cell delay variation tolerance (CDV Tolerance: hereinafter called CDVT) showing the allowable tolerance of CDV as a traffic, there is a possibility that a larger CDV than allowable CDV is contained for a virtual path or a virtual channel in which severe CDVT is defined.
For improving the QOS with improving the coefficient of utilization of the network resources, it is therefore necessary to realize a traffic shaping system which performs traffic shaping at the virtual path or virtual channel basis and output competition control considering the traffic characteristics of the virtual path or virtual channel.
An example of a conventional traffic shaper is described in an official gazette of Patent non-examined Publication No. Hei7-212367. The traffic shaper described in this official gazette identifies each of plurality of virtual channels included in the same virtual path by a virtual channel identifier (VCI), stores them in buffers classified by priority, and sending out cells so that the cell intervals become constant on the virtual path with performing an output competition control of cell by a priority control of buffer. In the priority control, cells in a buffer corresponding to a virtual channel in which sever CDV is defined are output preferentially, and it is intended to improve the coefficient of utilization of the network resources of the ATM network.
But in the conventional traffic shaper described in above official gazette, a technology of shaping for a virtual path basis was only disclosed, and shaping for a plurality of virtual channels in a virtual path was not disclosed. Besides, shaping for the single virtual path basis was only disclosed, and shaping dealing with plural virtual paths was not disclosed.
An example of another conventional traffic shaper is described in an official gazette of Patent non-examined Publication No. Hei8-163150. The traffic shaper described in this official gazette is provided immediately before a receiving terminal, and it is used for absorbing CDV of input cells of the receiving terminal. Therefore, a CDV absorption buffer in the receiving terminal is not required. In this traffic shaper, A CDV is removed by storing input cells in a shaping FIFO and reading out after elapsing a fixed time.
However, the conventional traffic shaper described in above official gazette is only applicable to a single input cell flow, and shaping of plural virtual paths or virtual channels are not mentioned. There was therefore a problem that shaping cell intervals for each virtual path or virtual channel was not performed. Besides, there was a problem that the coefficient of utilization of the network resources was not improved because no consideration was made for sending out cells by a priority order depending on allowable values of cell delay variation for a virtual channel.
The present invention aims, in view of the defects of the above conventional traffic shapers, to provide a traffic shaper in which cell delay variations of virtual paths or virtual channels are reduced to improve the coefficient of utilization of the network resources and traffic-shaping is performed by considering the priority of each virtual path or virtual channel for improving the quality of service of the virtual path or virtual channel.
Besides, the present invention aims to provide a traffic shaper in which traffic-shaping is performed by considering the priority of each virtual path or virtual channel based on the traffic characteristics of each virtual path or virtual channel.
Furthermore, the present invention aims to provide a traffic shaper in which traffic-shaping is performed by considering the priority of each virtual path or virtual channel based on the cell delay variation tolerance, that is one of the traffic characteristics, for more decreasing the cell delay variation of a virtual path or a virtual channel, in which a small cell delay variation tolerance is defined, in comparison with the cell delay variation of a virtual path or a virtual channel, in which a large cell delay variation tolerance is defined.
Furthermore, the present invention aims to provide a traffic shaper in which traffic-shaping is performed by considering the priority of each virtual path or virtual channel based on a peak cell rate (PCR), that is one of the traffic characteristics, for more decreasing the cell delay variation of a virtual path or a virtual channel, in which a cell flow of a large peak cell rate is contained, in comparison with the cell delay variation of a virtual path or a virtual channel, in which a cell flow of a small peak cell rate is contained.
A traffic shaper of the present invention dealing with plural virtual connections (general term of virtual path and virtual channel) for absorbing a cell delay variation of cell flow in each of virtual connections in an ATM (asynchronous transmission mode) network, and the traffic shaper comprises a cell identification part, a cell memory, a sending-out time determination part and a cell memory control part.
The cell identification part is provided for identifying a virtual connection allocated to an input cell, the cell memory is provided for storing input cells into respective virtual queues, each queue is corresponding to the virtual connection, in accordance with the identified virtual connection of each input cell, the sending-out time determination part is provided for determining a sending-out time for each cell stored in the cell memory on the virtual connection basis, and the cell memory control part is provided for performing a cell output from each virtual queue in accordance with the sending-out time determined for each cell, and performing an output competition control by selecting a cell to be output among cells having the same sending-out time in different virtual queues in accordance with a predetermined output priority assigned to each virtual connection.
Further, the cell memory control part comprises a priority table, a virtual queue state table and a cell sending-out control part, the priority table is provided for indicating the predetermined output priority for each virtual connection currently being established, the virtual queue state table is provided for indicating each virtual queue state including information of an existence of cell in the queue, sending-out scheduled time determined for the queue and a presence of cell sending-out request for the queue, and the cell sending-out control part is provided for setting a cell sending-out request for each virtual queue in the virtual queue state table when corresponding information indicating cell existence in the queue and the sending-out scheduled time is now or past, selecting a virtual queue, among virtual queues for which a cell sending-out request being set in the virtual queue state table, corresponding to the virtual connection having the highest predetermined output priority, and sending out a cell from the selected virtual queue.
Also, a traffic shaper of the present invention comprises a cell identification part, a sending-out time determination part, a cell memory and a cell memory control part.
The cell identification part is provided for identifying a virtual connection allocated to an input cell, the sending-out time determination part is provided for determining a sending-out time for each input cell on the virtual connection basis, the cell memory is provided for storing input cells into respective virtual queues, corresponding to the sending-out time, in accordance with determined time for each input cell, and the cell memory control part is provided for controlling a cell storage into respective virtual queues in accordance with the sending-out time determined for each cell and a predetermined output priority assigned to each virtual connection, and performing a cell output from each virtual queue in accordance with the sending-out time.
In this case, the cell memory control part further comprises a priority table, a sending-out time schedule table, a virtual queue state table, a cell write control part and a cell reading-out control part.
The priority table is provided for indicating the predetermined output priority for each virtual connection currently being established, the sending-out time schedule table is provided for indicating sending-out scheduled time determined for each virtual connection, the virtual queue state table is provided for indicating an existence of cell in each virtual queue, the cell write control part is provided for controlling a cell storage into respective virtual queues in accordance with the sending-out time determined for each cell and a predetermined output priority assigned to each virtual connection, and the cell reading-out control part is provided for reading-out a cell in the virtual queue indicated by a sequential reading-out pointer, and sending out the cell.
The predetermined output priority assigned to each virtual connection can be determined by an allowable cell delay variation tolerance for each virtual channel.
The predetermined output priority assigned to each virtual connection can be determined by an allowable peak cell rate for each virtual channel.